Devices and methods for performing in-vivo imaging of passages or cavities within a body are known in the art. Such devices may include, inter alia, various endoscopic imaging systems and devices for performing imaging in various internal body cavities.
Reference is now made to FIG. 1 which is a schematic diagram illustrating an embodiment of an autonomous in-vivo imaging device. The device 10A typically includes an optical window 21 and an imaging system for obtaining images from inside a body cavity or lumen, such as the GI tract. The imaging system includes an illumination unit 23. The illumination unit 23 may include one or more discrete light sources 23A, or may include only one light source 23A. The one or more light sources 23A may be a white light emitting diode (LED), or any other suitable light source, known in the art. The device 10A includes a CMOS imaging sensor 24, which acquires the images and an optical system 22 which focuses the images onto the CMOS imaging sensor 24. The illumination unit 23 illuminates the inner portions of the body lumen through an optical window 21. Device 10A further includes a transmitter 26 and an antenna 27 for transmitting the video signal of the CMOS imaging sensor 24, and one or more power sources 25. The power source(s) 25 may be any suitable power sources such as but not limited to silver oxide batteries, lithium batteries, or other electrochemical cells having a high energy density, or the like. The power source(s) 25 may provide power to the electrical elements of the device 10A.
Typically, in the gastrointestinal application, as the device 10A is transported through the gastrointestinal (GI) tract, the imager, such as but not limited to the multi-pixel CMOS sensor 24 of the device 10A acquires images (frames) which are processed and transmitted to an external receiver/recorder (not shown) worn by the patient for recording and storage. The recorded data may then be downloaded from the receiver/recorder to a computer or workstation (not shown) for display and analysis. Other systems and methods may also be suitable.
During the movement of the device 10A through the GI tract, the imager may acquire frames at a fixed or at a variable frame acquisition rate. For example, the imager (such as, but not limited to the CMOS sensor 24 of FIG. 1) may acquire images at a fixed rate of two frames per second (2 Hz). However, other different frame rates may also be used, depending, inter alia, on the type and characteristics of the specific imager or camera or sensor array implementation that is used, and on the available transmission bandwidth of the transmitter 26. The downloaded images may be displayed by the workstation by replaying them at a desired frame rate. According to this implementation, the expert or physician examining the data may be provided with a movie-like video playback, which may enable the physician to review the passage of the device through the GI tract.
One of the limitations of electronic imaging sensors is that they may have a limited dynamic range. The dynamic range of most existing electronic imaging sensors is significantly lower than the dynamic range of the human eye. Thus, when the imaged field of view includes both dark and bright parts or imaged objects, the limited dynamic range of the imaging sensor may result in underexposure of the dark parts of the field of view, or overexposure of the bright parts of the field of view, or both.
Various methods may be used for increasing the dynamic range of an imager. Such methods may include changing the amount of light reaching the imaging sensor, such as for example by changing the diameter of an iris or diaphragm included in the imaging device to increase or decrease the amount of light reaching the imaging sensor, methods for changing the exposure time, methods for changing the gain of the imager or methods for changing the intensity of the illumination. For example, in still cameras, the intensity of the flash unit may be changed during the exposure of the film.
When a series of consecutive frames is imaged such as in video cameras, the intensity of illumination of the imaged field of view within the currently imaged frame may be modified based on the results of measurement of light intensity performed in one or more previous frames. This method is based on the assumption that the illumination conditions do not change abruptly from one frame to the consecutive frame.
However, in an in vivo imaging device, for example, for imaging the GI tract, which may operate at low frame rates and which is moved through a body lumen (e.g., propelled by the peristaltic movements of the intestinal walls), the illumination conditions may vary significantly from one frame to the next frame. Therefore, methods of controlling the illumination based on analysis of data or measurement results of previous frames may not be always feasible, particularly at low frame rates.
Therefore there is a need for an imaging device that provides more accurate illumination, possibly tailored to particular in-vivo illumination requirements or environmental conditions.